Helically shaped inserts are frequently added to heated energy systems, such as furnaces, boilers, and other systems that use radiant tubes, and to catalytic systems, to fuel cells, and to other systems that convert hydrocarbon fuels into usable forms of energy. The addition of helical inserts is advantageous for many reasons, which include enhanced fluid channeling, uniformity of heat transfer and radiation, the moderation of fluid flow and energy-producing reactions, the control and enhancement of energy-producing reactions, system structural enhancement, and increased system efficiency.
Helical inserts are typically positioned within heated energy systems to interact with and/or to be exposed to the products of energy generation, such as combusted hydrocarbon fuel, steam, hydrogen, nitrogen, carbon dioxide, and the products of catalytic reactions, subjecting the inserts to high temperature environments. Heated energy systems often have operating temperatures in the approximate range of about 600° to 2500° F. Inserts must therefore normally be capable of withstanding such high temperature environments.
If heat produced by energy-producing reactions within a system is not properly radiated, captured or recycled due to an inefficiency of the helical insert or of the system as a whole, an undue amount of energy may be lost and wasted or possibly result in a lack of control, economy, or operability of the system. Therefore, when helical inserts are incorporated into energy systems and positioned in the vicinities of high levels of heat energy, helical inserts can also be configured to function as components of heat exchanging systems that absorb and productively use the heat energy produced. This type of insert is often referred to as a heat exchanger. Typically, a heat exchanger will be either fabricated or modified to include a fluid inlet to allow for the entry of a heat exchanging fluid, a fluid channel to allow for the transfer of heat energy to the heat exchanging fluid through the heat exchanger's outer walls, and a fluid outlet to allow for the expulsion of heated heat exchanging fluid. Heat exchanging is normally performed in a manner that prevents the mixing of the heat exchanging fluid and the products of energy generation while the heat exchanging fluid is within the heat exchanger.
Ceramics have been used as construction materials for non-heat exchanging inserts in some systems due to the natural capability of ceramics to withstand high temperature environments. Ceramic inserts are advantageous in that they generally experience less thermal expansion than do other materials when subjected to significant temperature changes. The reduced thermal expansion rates of ceramics can also enhance the ability of a helical insert to match and couple with other system components, reducing thermally-induced stresses that can be associated with intercomponent couplings during high temperature operating conditions.
Helical heat exchangers that have been incorporated into heated energy systems have been constructed of metal materials, such as nickel-chrome alloy. One reason for this is that metals are much easier to fabricate into helically twisted shapes, especially for simple, low twist geometries that allow the efficient exchanging of heat energy to a heat exchanging fluid flowing within the heat exchangers. However, metals exhibit far greater levels of thermal expansion and operate at lower temperatures than do their ceramic counterparts. These characteristics can potentially limit the ability of a metal helical insert to function without adversely affecting other components of a heated energy system.
Although both ceramic and metal materials can pose difficulties in the fabrication of helical inserts that require highly complex shaping, it is believed that ceramics generally allow for greater flexibility than metals in the fabrication of complex insert shapes. Thus, ceramic insert fabrication techniques are often preferred where it is feasible to use them.
When multiple helical inserts are used in a heated energy system, the positioning of multiple inserts that are parallel to each other at a particular location along a single path of products of energy generation can be problematic. In general, overall tooling costs are higher for multiple parallel helical inserts. For example, if multiple parallel inserts are formed or manufactured simultaneously, costly additional or repetitive fabrication equipment may be required which complicate manufacturing processes. Tooling and production costs are also often higher as a result.
If multiple parallel helical heat exchangers are manufactured individually, but are later coupled and/or manifolded in parallel, such coupling and/or manifolding typically results in substantial increases in apparatus cost. Since coupling and/or manifolding components are frequently made of metal, the above-noted problems associated with metal thermal expansion can also have adverse effects on the heated energy system. For example, intercomponent thermal expansion could result in some components breaking or cracking, and if heat exchanging fluid is being used, loss or leakage of fluid from the insert or contamination of the heat exchanging fluid by the products of energy generation.
After a helical insert is fabricated and implemented within a heated energy system, the interaction of the insert with the energy system depends on factors such as insert size, insert shape, the relative positioning of the insert within the system, and the manner in which the insert is configured to interact with energy-producing reactions and/or with the products of those reactions. The presence of multiple parallel helical inserts can cause products of energy generation to migrate or be shared between multiple helical paths, reducing the overall interaction with individual inserts and reducing the efficiency of heat radiation and/or heat transfer in heat exchanging processes. Thus, to maximize heat transfer to a heat exchanging fluid, it is considered advantageous to require products of energy generation to flow through the spiral paths as few helical heat exchangers as possible along a particular length of a fluid path for products of energy generation, while still effectively operating the heat exchanging system.